Compositions comprising eutectic metal alloy nanoparticles

ABSTRACT

Provided herein is a composition for eutectic metal alloy nanoparticles having an average particle size ranging from about 0.5 nanometers to less than about 5000 nanometers and at least one organoamine stabilizer. Also provided herein is a process for preparing eutectic metal alloy nanoparticles comprising mixing at least one organic polar solvent, at least one organoamine stabilizer, and a eutectic metal alloy to create a mixture; sonicating the mixture at a temperature above the melting point of the eutectic metal alloy; and collecting a composition comprising a plurality of eutectic metal alloy nanoparticles having an average particle size ranging from about 0.5 nanometers to less than about 5000 nanometers. Further disclosed herein are hybrid conductive ink compositions comprising a component comprising a plurality of metal nanoparticles and a component comprising a plurality of eutectic metal alloy nanoparticles.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 16/277,545filed Feb. 15, 2019, now allowed, which claims the benefit of U.S.Provisional Application No. 62/713,848, filed Aug. 2, 2018, thedisclosures of which are incorporated herein by reference in theirentirety.

FIELD OF THE DISCLOSURE

This disclosure relates generally to eutectic metal alloy nanoparticlesand compositions for conductive inks comprising eutectic metal alloynanoparticles. The eutectic metal alloy nanoparticles disclosed hereinmay be prepared by mixing at least one solvent, at least one organoaminestabilizer, and a eutectic metal alloy to create a mixture, and thensonicating the mixture to create a dispersion comprising eutectic metalalloy nanoparticles. Further disclosed herein is a conductive inkcomposition comprising a plurality of silver nanoparticles and aplurality of eutectic metal nanoparticles, wherein the eutectic metalnanoparticles have an average particle size ranging from about 0.5nanometers to less than about 1000 nanometers.

BACKGROUND

Printed electronics, or the fabrication of electronic components usingliquid deposition techniques, has recently become of great interest.Such techniques may provide potentially low-cost alternatives toconventional mainstream amorphous silicon technologies for electronicapplications such as thin film transistors (TFTs), light-emitting diodes(LEDs), RFID tags, photovoltaics, printed memory, and the like. However,it has been a challenge to meet the conductivity, processing,morphology, and cost requirements for practical applications of printedelectronics using liquids.

Traditional processes for the fabrication of electronic circuit elementsrequire high temperature and pressure. Accordingly, conductive elementssuch as interconnects are typically formed on rigid surfaces, such assilicon. High temperatures and pressures limit the use of materialsavailable for printed electronics, which may, for example, use flexibleplastic substrates that melt at low temperatures, such as at about 150°C. or less.

Certain electrically conductive materials are known in the art for lowmelting temperatures and thus may be suitable for use on a wide range ofsubstrates, including flexible plastic substrates. For example, inkscomprising silver nanoparticles may have a high silver content, lowviscosity, and melting temperature less than or equal to about 145° C.Thus inks comprising silver nanoparticles are capable of formingconductive elements by bonding (sintering) the silver particle at lowtemperatures.

Despite these benefits, however, silver nanoparticle inks alone often donot provide sufficient adhesion to bond electronic components to theunderlying circuitry or substrates, thus limiting their use asinterconnects.

Certain liquid metals have been identified as potentially usefulmaterials for conductive inks and for use with flexible printedelectronics. These liquid metals, which may include, for example,gallium, indium, bismuth, and tin, may be added to conductive inks, suchas silver nanoparticle inks, to create hybrid conductive inks. Liquidmetal particles, however, due to their larger size and high density, mayresult in poorly dispersed compositions, as well as poor jettability ofthe resultant ink composition.

There is thus a need in the art for jettable ink compositions thatenable printing and are suitable for fabricating interconnects as wellas conductive features such as traces, electrodes, and the like on avariety of substrates, including flexible plastic substrates.

SUMMARY

Disclosed herein are eutectic metal alloy nanoparticles suitable for usein conductive inks. In one embodiment, there is provided a compositioncomprising a plurality of eutectic metal alloy nanoparticles having anaverage particle size ranging from about 0.5 nanometers to less thanabout 5000 nanometers, such as from about 0.5 nanometers to about 1000nanometers or about 50 nanometers to about 800 nanometers, and at leastone organoamine stabilizer. In certain embodiments, the eutectic metalalloy nanoparticles comprise Field's metal alloy, and in certainembodiments, the composition does not comprise metal nanoparticles, suchas silver nanoparticles.

In certain embodiments, the composition further comprises at least oneorganic polar solvent, such as at least one of propylene glycol methylether acetate, di(propylene glycol) methyl ether acetate, (propyleneglycol) methyl ether, di(propylene glycol) methyl ether, methyl isobutylketone, and diisobutyl ketone. In certain embodiments, the at least oneorganic polar solvent is propylene glycol methyl ether acetate. Invarious embodiments of the disclosure, the eutectic metal alloynanoparticles have an average particle size ranging from about 50nanometers to about 400 nanometers, such as from about 100 nanometers toabout 250 nanometers. According to certain embodiments, the at least oneorganoamine stabilizer is chosen from butylamine, octylamine,3-methoxypropylamine, pentaethylenehexamine,2,2-(ethylenedioxy)diethylamine, tetraethylenepentamine,triethylenetetramine, and diethylenetriamine.

In yet another embodiment, disclosed herein are processes for preparinga composition for conductive inks, the process comprising the steps ofmixing at least one organic polar solvent, at least one organoaminestabilizer, and a eutectic metal alloy to create a mixture; sonicatingthe mixture to create a dispersion comprising a plurality of eutecticmetal alloy nanoparticles having an average particle size ranging fromabout 0.5 nanometers to less than about 5000 nanometers, such as fromabout 0.5 nanometers to less than about 1000 nanometers, from about 50nanometers to about 800 nanometers, or from about 100 nanometers toabout 500 nanometers. According to certain embodiments, the eutecticmetal alloy nanoparticles comprise Field's metal alloy.

In certain embodiments of the processes disclosed herein, the at leastone organic polar solvent is heated to a temperature ranging from about50° C. to about 75° C., and in certain embodiments, the mixture issonicated for a period of time ranging from about 1 minute to about 1hour at 100% power. In certain embodiments, the composition is collectedby centrifuging the dispersion and decanting the at least one organicpolar solvent.

Further disclosed herein are hybrid conductive ink compositionscomprising a component comprising a plurality of metal nanoparticles anda component comprising a plurality of eutectic metal alloy nanoparticlesand at least one organoamine stabilizer, wherein the eutectic metalalloy nanoparticles have an average particle size ranging from about 0.5nanometers to less than about 1000 nanometers, such as from about 50nanometers to about 400 nanometers.

According to certain embodiments of the hybrid conductive ink disclosedherein, the plurality of metal nanoparticles is silver nanoparticles,and in certain embodiments, the silver nanoparticles have an averageparticle size ranging from about 0.5 nanometers to about 100 nanometers.In certain embodiments of the hybrid conductive ink disclosed herein,the eutectic metal alloy nanoparticle is Field's metal alloy, and incertain embodiments, the weight ratio of the eutectic metal alloynanoparticles and the metal nanoparticles ranges from about 1:20 toabout 1:5. In various embodiments disclosed herein, the hybridconductive ink has a viscosity ranging from about 2 centipoise (cps) toabout 200 cps.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the present teachings, as claimed.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to embodiments of the presentdisclosure. The following description is merely exemplary.

Disclosed herein are compositions comprising eutectic metal alloynanoparticles. As used herein, the term “eutectic” refers to a mixtureor an alloy in which the constituent parts are present in suchproportions that the constituents melt simultaneously, and the meltingpoint is lower than either of the constituents individually. The term“melting point,” as used herein, refers to the temperature at which asolid becomes a liquid at atmospheric pressure. The term “alloy,” asused herein, refers to a mixture containing two or more metals, and,optionally, additional non-metals, wherein the elements of the alloy arefused together or dissolved into each other when molten. Accordingly, aeutectic metal alloy solidifies at a single temperature and meltscompletely at one temperature, the eutectic point.

In certain embodiments, the eutectic metal alloy nanoparticlecompositions disclosed herein may be added to metal nanoparticles, suchas silver nanoparticles, or a composition comprising metalnanoparticles, to form a hybrid conductive ink containing a plurality ofsilver nanoparticles and a plurality of eutectic metal alloynanoparticles. These inks may retain electrical conductivity comparableto conventional nanosilver inks, even though they may be formulated withless silver, such as up to 20% less silver and, accordingly, can bemanufactured at a reduced cost. The hybrid conductive ink compositionsdisclosed herein may also be suitable for use with jetting applications,including aerosol jet printing, and may be used to form self-healingconductive elements at low sintering temperatures. Accordingly, thehybrid conductive ink compositions disclosed herein are suitable for usewith a variety of substrates, including low-melting point plastics.These hybrid conductive inks, unlike conventional nanosilver inks, mayalso be useful as a solder to form robust interconnects at lowtemperatures.

The nanometer size of the eutectic metal alloy nanoparticles disclosedherein, along with their ligand functionalization, may allow theeutectic metal alloy nanoparticles to be well-dispersed into jettableink formulations. In certain embodiments, the hybrid conductive inkcomposition comprising eutectic metal alloy nanoparticles may have ameasured conductivity greater than about 1000 S/cm, have a high adhesivestrength, a curing temperature less than about 120° C., and a curingtime less than about 2 hours.

The eutectic metal alloy nanoparticles disclosed herein may comprise theeutectic alloy Field's metal (bismuth, indium, and tin). In certainembodiments, the weight ratio of the eutectic metal alloy nanoparticlesand the metal nanoparticles in a hybrid conductive ink may range fromabout 1:20 to about 1:5.

Also provided herein is a method of forming an interconnect, including:a) depositing a hybrid conductive ink on a conductive element positionedon a substrate, wherein the hybrid conductive ink includes a pluralityof silver nanoparticles and a plurality of eutectic metal alloynanoparticles; b) placing an electronic component onto the hybridconductive ink; and c) heating the substrate, conductive element, hybridconductive ink and electronic component to a temperature sufficient i)to anneal the plurality of silver nanoparticles in the hybrid conductiveink and ii) to melt the plurality of eutectic metal alloy nanoparticlesto form a melted eutectic alloy, wherein the melted eutectic alloy flowsto occupy spaces between the annealed plurality of silver nanoparticles,d) allowing the melted eutectic alloy of the hybrid conductive ink toharden and fuse to the electronic component and the conductive element,thereby forming the interconnect.

Eutectic Metal Alloys

In certain embodiments, disclosed herein are compositions comprising atleast one organoamine stabilizer and a plurality of eutectic metal alloynanoparticles. To prepare the compositions disclosed herein comprising aplurality of eutectic metal alloy nanoparticles, a suitable eutecticmetal alloy may be added to at least one polar solvent and the at leastone organoamine stabilizer.

Suitable eutectic metal alloys for use in the present compositioninclude those eutectic metal alloys having a melting point lower thanthat of the melting point of the substrate upon which a conductive inkcomposition may be deposited and sintered. For example, in certainembodiments, the melting points of suitable eutectic metal alloys may beabout 140° C. or less, such as about 55° C. to about 75° C., about 60°C. to about 65° C., or about 62° C. Eutectic metal alloys may becomprised of, for example, at least two metals chosen from bismuth,lead, tin, cadium, zinc, indium, gallium, and thallium. For example, theeutectic metal alloys may include at least two of bismuth, tin, indium,and gallium, or, in certain embodiments, the eutectic metal alloydisclosed herein may include indium, bismuth, and tin. In certainembodiments, the eutectic metal alloy is chosen fromIn_(51.0)Bi_(32.5)Sn_(16.5), i.e., Field's Metal (melting point 62° C.),Bi₅₈Sn₄₂ (melting point 138° C.), In_(66.3)Bi_(33.7) (melting point 72°C.), and Bi₅₇Sn₄₃ (melting point 139° C.). As used herein, “Field'smetal” refers to a eutectic, low-melting alloy of bismuth, indium, andtin, that is In_(51.0)Bi_(32.5)Sn_(16.5). In other embodiments disclosedherein, the eutectic metal alloy may further include at least oneorganic vehicle, such as an organic solvent and/or a stabilizer asdescribed herein for the silver nanoparticle component.

Organoamine Stabilizers

In some embodiments, the component comprising a plurality of eutecticmetal alloy nanoparticles further comprises at least one organicstabilizer. The organic stabilizer may be physically or chemicallyassociated with the surface of the eutectic metal alloy nanoparticles.In this way, the nanoparticles have the stabilizer thereon outside of aliquid solution. That is, the nanoparticles with the stabilizer thereonmay be isolated and recovered from a reaction mixture solution used informing the nanoparticles and stabilizer complex. The stabilizednanoparticles may thus be subsequently ready and homogenously dispersedin a solvent for forming a hybrid conductive ink composition.

The organic stabilizer may interact with the eutectic metal alloynanoparticle by a chemical bond and/or a physical attachment. Thechemical bond may take the form of, for example, covalent bonding,hydrogen bonding, coordination complex bonding, ionic bonding, or amixture of different chemical bonds. The physical attachment may takethe form of, for example, van der Waals' forces, dipole-dipoleinteractions, or a mixture of different physical attachments.

The term “organic” in “organic stabilizer” refers to, for example, thepresence of carbon, but, in addition to carbon, the organic stabilizermay include one or more non-metal heteroatoms such as nitrogen, oxygen,sulfur, silicon, halogen, and the like.

Exemplary organic stabilizers can include organoamines such aspropylamine, butylamine, pentylamine, hexylamine, heptylamine,octylamine, nonylamine, decylamine, undecylamine, tridecylamine,tetradecylamine, pentadecylamine, hexadecylamine, heptadecylamine,octadecylamine, N,N-dimethylamine, N,N-dipropylamine, N,N-dibutylamine,N,N-dipentylamine, N,N-dihexylamine, N,N-diheptylamine,N,N-dioctylamine, N,N-dinonylamine, N,N-didecylamine,N,N-diundecylamine, N,N-didodecylamine, dodecylamine, methylpropylamine,ethylpropylamine, propylbutylamine, ethylbutylamine, ethylpentylamine,propylpentylamine, butylpentylamine, triethylamine, tripropylamine,tributylamine, tripentylamine, trihexylamine, triheptylamine,trioctylamine, 1,2-ethylenediamine,N,N,N′,N′-tetramethylethylenediamine, propane-1,3-diamine,N,N,N′,N′-tetramethylpropane-1,3-diamine, butane-1,4-diamine,N,N,N′,N′-tetramethylbutane-1,4-diamine, diaminopentane, diaminoheptane,diaminooctane, diaminononane, diaminodecane,2,2-(ethylenedioxy)diethylamine, 3-methoxypropylamine,pentaethylenehexamine, tetraethylenepentamine, and the like or mixturesthereof. Exemplary organoamine stabilizers include butylamine,octylamine, 2,2-(ethylenedioxy)diethylamine, 3-methoxypropylamine,pentaethylenehexamine, and tetraethylenepentamine.

The extent of the coverage of the at least one organoamine stabilizer onthe surface of the eutectic metal alloy nanoparticles may vary, forexample, from partial to full coverage depending on the capability ofthe organoamine stabilizer to stabilize the nanoparticles.

Organic Polar Solvents

In certain embodiments, the composition comprising a plurality ofeutectic metal alloy nanoparticles further comprises at least oneorganic polar solvent. According to various embodiments disclosedherein, the solvent is not water, and in certain embodiments, thecomposition comprising a plurality of eutectic metal alloy nanoparticlesis free of water. As used herein, “free of water,” indicates that thecomposition does not contain a detectable quantity of water or that thecomposition is anhydrous.

Exemplary suitable organic polar solvents may include propylene glycolmethyl ether acetate, propylene glycol monomethyl ether acetate,toluene, di(propylene glycol) methyl ether acetate, (propylene glycol)methyl ether, di(propylene glycol) methyl ether, methyl isobutyl ketone,diisobutyl ketone, butyl acetate, methoxypropylacetate, propoxylatedneopentylglycoldiacrylate, 1-phenoxy-2-propanol, and combinationsthereof. In certain embodiments, the at least one polar solvent ispropylene glycol methyl ether acetate.

Eutectic Metal Alloy Nanoparticles

The eutectic metal alloy nanoparticle composition disclosed herein maybe prepared by any suitable method. One exemplary method is to addpieces, such as centimeter sized chunks, of the eutectic metal alloydisclosed herein to a heated mixture comprising at least one solvent andat least one organoamine stabilizer until the alloy is molten and amixture is formed. The mixture may then be dispersed by sonication andcooled. The eutectic metal alloy nanoparticles may then be isolated bydecantation, rinsed, and dried.

Prior to, during, or after mixing the at least one organoaminestabilizer to the at least one solvent, the solvent may be heated, forexample, to a temperature above the melting point of the eutectic metalalloy nanoparticles. In certain embodiments, the solvent may be heatedto a temperature greater than about 55° C., such as about 60° C., about65° C., about 70° C., about 75° C., or about 80° C.

The sonication can be performed by probe sonication or by bathsonication. Probe sonication refers to sonication wherein a probe isinserted into a container containing the mixture. Bath sonication refersto sonication wherein the container containing the mixture is placedinto a bath, and the bath is subsequently sonicated. Probe sonicationmay provide greater energy/power compared to bath sonication.

In certain embodiments, the mixture may be sonicated at any suitablepower, such as a power ranging from about 20% to about 100%, such asabout 50% to about 90%, about 60% to about 80%, or, in certainembodiments, at about 100% power. The mixture may be sonicated for anysuitable amount of time, such as, for example, from about 1 minute toabout 1 hour, or, in certain embodiments, from about 2 minutes to about45 minutes, about 5 minutes to about 20 minutes, or about 8 minutes toabout 15 minutes. Any desired or effective sonicator can be used, suchas a Branson Digital Probe Sonifier®. During sonication, the dispersionmay be iced in order to cool the dispersion. In certain embodiments, thedispersion may be placed in an ice bath while sonicating in order tomaintain the temperature of the dispersion below a certain temperature,such as, for example, below about 100° C., below about 85° C., or belowabout 75° C. After sonication, the dispersion may be cooled, for examplecooled to about room temperature. The dispersed nanoparticles may thenbe collected, for example by centrifucation and decantation of thesolvent, which may be repeated as necessary. Finally, the nanoparticlesmay be dried.

The average diameter of the eutectic metal alloy nanoparticles may beabout 1000 nanometers (nm) or less. In certain embodiments, the averageparticle size of the eutectic metal alloy nanoparticles may range fromabout 0.5 nm to about 1000 nm or from about 0.5 nm to less than about1000 nm, such as from about 1 nm to about 750 nm, from about 10 nm toabout 500 nm, from about 50 nm to about 400, from about 75 nm to about250 nm, from about 100 nm to about 200 nm, or from about 100 nm to about150 nm. In certain embodiments, the median diameter (D50) of theeutectic metal alloy nanoparticles may range from about 0.5 nm to about1000 nm or from about 0.5 nm to less than about 1000 nm, such as fromabout 1 nm to about 750 nm, from about 10 nm to about 500 nm, from about50 nm to about 400, from about 75 nm to about 250 nm, from about 100 nmto about 225 nm, or from about 150 nm to about 200 nm. The averageparticle size and diameter of the particles may be determined by anysuitable means, such as, for example, light microscopy, ScanningElectron Microscopy (SEM), or, for example, by using a Nanotrac®particle size analyzer.

Hybrid Conductive Ink Compositions

The hybrid conductive inks disclosed herein may include a componentcomprising a plurality of eutectic metal alloy nanoparticles and acomponent comprising a plurality of metal nanoparticles, such as silvernanoparticles. The component comprising a plurality of metalnanoparticles contains silver nanoparticles and optionally at least oneof solvents, stabilizers, and other additives.

The metal nanoparticles, such as silver nanoparticles, disclosed hereinmay have any shape or geometry, for example spherical. In certainembodiments, the silver nanoparticles have a volume average particlediameter ranging from about 0.5 nm to about 100 nm, such as from about 1nm to about 50 nm, or from about 1 nm to about 20 nm. Volume averageparticle size may be measured by any suitable means, such as a lightscattering particle sizer, a Transmission Electron Microscope or aBeckman Coulter Multisizer 3 (Beckman Coulter Inc., Life SciencesDivision, Indianapolis, Ind.). In certain embodiments, volume averageparticle size of the present silver nanoparticles may be measured viadynamic light scattering using a Malvern Nano ZS Zetasizer Model 3600(Malvern Instruments Ltd., Worcestershire, UK).

As used herein, the particle size distribution width refers to thedifference between the diameter of the largest nanoparticle and thediameter of the smallest nanoparticle, or the range between the smallestand the largest nanoparticle. In certain embodiments, the particle sizedistribution width of the silver nanoparticles is about 30 nm or less,such as from about 10 nm to about 30 nm, or from about 10 nm to about 25nm.

The silver nanoparticles disclosed herein may, in certain embodiments,have properties distinguishable from those of silver flakes. Forexample, the silver nanoparticles disclosed herein may be characterizedby enhanced reactivity of the surface atoms and high electricalconductivity. Further, the present silver nanoparticles may have a lowermelting point and a lower sintering temperature than silver flakes. Theterm “sintering” refers to a process in which adjacent surfaces of metalpowder particles are bonded by heating, i.e., “annealed.” This is incontrast to micron-sized metal flakes, where the mode of conductivity isvia ohmic contact through particle-particle touching and overlap. Theseflake-based inks may have conductivities several orders of magnitudelower than sintered nanoparticle conductive inks that melt together.

Due to their small size, silver nanoparticles may exhibit a meltingpoint as low as 700° C. below that of silver flakes. In someembodiments, the silver nanoparticles of the hybrid conductive inksdisclosed herein may sinter at temperatures greater than 800° C. belowthat of bulk silver (mp=961.8° C.) In certain embodiments, the silvernanoparticles of the present disclosure sinter at a temperature rangingfrom about 80° C. to about 250° C., such as from about 145° C. or less,or at about 140° C. or less, such as at about 130° C. or at about 120°C.

Although not wishing to be bound by theory, it is believed that thelower melting point of the silver nanoparticles disclosed herein is aresult of their comparatively high surface-area-to-volume ratio, whichallows bonds to readily form between neighboring particles. The largereduction in sintering temperature for metal nanoparticles enables theformation of highly conductive circuit traces or patterns on flexibleplastic substrates since such substrates, e.g., polycarbonatesubstrates, may melt or soften at a relatively low temperature (forexample, at about 150° C.).

The silver nanoparticles disclosed herein may comprise elemental silver,a silver alloy, a silver compound or combinations thereof. In certainembodiments, the silver nanoparticles may be a base material coated orplated with pure silver, a silver alloy or a silver compound. Forexample, the base material may be copper nanoparticles with a silvercoating.

Silver alloys of the present disclosure may be formed from at least onemetal selected from Au, Cu, Ni, Co, Pd, Pt, Ti, V, Mn, Fe, Cr, Zr, Nb,Mo, W, Ru, Cd, Ta, Re, Os, Ir, Al, Ga, Ge, In, Sn, Sb, Pb, Bi, Si, As,Hg, Sm, Eu, Th, Mg, Ca, Sr, and Ba. Exemplary metal composites areAu—Ag, Ag—Cu, Au—Ag—Cu, and Au—Ag—Pd. In certain embodiments, the metalcomposites may further include at least one non-metal, such as, forexample, Si, C, and Ge. Suitable silver compounds may include, forexample, silver oxide, silver thiocyanate, silver cyanide, silvercyanate, silver carbonate, silver nitrate, silver nitrite, silversulfate, silver phosphate, silver perchlorate, silver tetrafluoroborate,silver acetylacetonate, silver acetate, silver lactate, silver oxalate,and derivatives thereof. In certain embodiments, the silvernanoparticles comprise elemental silver.

In addition to silver nanoparticles, the silver nanoparticle componentof the hybrid conductive ink composition disclosed herein may alsoinclude at least one organic vehicle. In certain embodiments, theconstituents of the at least one organic vehicle may be selected bythose having ordinary skill in the art, in accordance with the presentdisclosure for the hybrid conductive ink, to meet specific deposition,processing, adhesion and/or other performance characteristics. Forinstance, in an application in which the present hybrid conductive inkcompositions are employed as a solder paste replacement, the organicvehicle may be formulated to volatize during processing. In applicationsin which the present hybrid conductive ink compositions are employed inadherent coatings on nonmetallic surfaces, the organic vehicle may beselected for adhesive properties.

In some embodiments, the organic vehicle comprises a solvent to dispersethe silver nanoparticles. The solvent may be, for example, a non-polarorganic solvent. Suitable non-polar organic solvents include, forexample, hydrocarbons such as alkanes; alkenes; alcohols having fromabout 10 to about 18 carbons such as undecane, dodecane, tridecane,tetradecane, hexadecane, 1-undecanol, 2-undecanol, 3-undecanol,4-undecanol, 5-undecanol, 6-undecanol, 1-dodecanol, 2-dodecanol,3-dodecanol, 4-dodecanol, 5-dodecanol, 6-dodecanol, 1-tridecanol,2-tetradecanol, 3-tetradecanol, 4-tetradecanol, 5-tetradecanol,6-tetradecanol, 7-tetradecanol, and the like; alcohols, such as forexample, terpineol (α-terpineol), β-terpineol, geraniol, cineol, cedral,linalool, 4-terpineol, lavandulol, citronellol, nerol, methol, borneol,hexanol, heptanol, cyclohexanol, 3,7-dimethylocta-2,6-dien-1-ol, and2-(2-propyl)-5-methyl-cyclohexane-1-ol; isoparaffinic hydrocarbons suchas isodecane, isododecane, and commercially available mixtures ofisoparaffins such as Isopar® E, Isopar® C., Isopar® L, Isopar® V, andIsopar® M, manufactured by Exxon Chemical Company Inc. (Spring, Tex.);Shellsol®, manufactured by Shell Chemical Company (The Hague,Netherlands); Soltrol®, manufactured by Philips Oil Co., Ltd. (TheWoodlands, Tex.); Begasol®, manufactured by Mobil Petroleum Co., Inc.(Spring, Tex.); IP Solvent 2835, made by Idemitsu Petrochemical Co.,Ltd. (Tokyo, JP); naphthenic oils; aromatic solvents such as benzene,nitrobenzene, toluene, ortho-, meta-, and para-xylene, and mixturesthereof; 1,3,5-trimethylbenzene (mesitylene); 1,2-, 1,3-, and1,4-dichlorobenzene, and mixtures thereof; trichlorobenzene;cyanobenzene; ethylcyclohexane, phenylcyclohexane, and tetralin;aliphatic solvents, such as hexane, heptane, octane, isooctane, nonane,decane, and dodecane; and cyclic aliphatic solvents, such asbicyclohexyl and decalin. In certain embodiments, two or more non-polarorganic solvents may be used as dispersion agents, and in certainembodiments, the non-polar organic solvents included in the silvernanoparticle component are ethylcyclohexane and phenylcyclohexane.

The at least one non-polar organic solvent may be present in the silvernanoparticle composition in an amount, for example, ranging from about 5weight percent to about 50 weight percent, such as from about 10 weightpercent to about 40 weight percent, from about 10 weight percent toabout 40 weight percent, about 36 weight percent, or from about 10weight percent to about 26 weight percent, based on the total weight ofthe silver nanoparticle ink component. As a result, the weightpercentage of silver nanoparticles in the silver nanoparticle inkcomposition may range, for example, from about 95 weight percent toabout 50 weight percent, from about 90 weight percent to about 64 weightpercent, from about 90 weight percent to about 74 weight percent.

In some embodiments, the at least one organic vehicle comprises at leastone stabilizer. In certain embodiments, the at least one stabilizer mayinteract with the silver nanoparticles by chemical bond and/or aphysical attachment. The chemical bond may take the form of, forexample, covalent bonding, hydrogen bonding, coordination complexbonding, ionic bonding or a mixture of different chemical bondings. Thephysical attachment may take the form of, for example, van der Waals'forces, dipole-dipole interaction, or a mixture of different physicalattachments. In addition, the at least one stabilizer may be thermallyremovable, which means that the at least one stabilizer may disassociatefrom a silver-containing nanoparticle surface under certain conditions,such as through heating or annealing.

Suitable stabilizers include at least one organic stabilizer as definedabove for eutectic metal alloy nanoparticles. In certain embodiments,the silver nanoparticles are stabilized with at least one of octylamine,nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine,tetradecylamine, pentadecylamine, or hexadecylamine.

The weight percentage of the at least one organic stabilizer in thesilver nanoparticle component (including only the silver nanoparticlesand the at least one stabilizer and excluding the at least one solvent)may range from, for example, about 3 weight percent to about 60 weightpercent, from about 5 weight percent to about 35 weight percent, fromabout 5 weight percent to about 20 weight percent, or from about 5weight percent to about 10 weight percent. As a result, the weightpercentage of the silver in the silver nanoparticles (excluding the atleast one solvent) may range from, for example, about 40 weight percentto about 97 weight percent, from about 65 weight percent to about 95weight percent, from about 80 weight percent to about 95 weight percent,or from about 90 weight percent to about 95 weight percent.

The silver nanoparticle component may further include at least one resinto improve adhesion to substrates. For example, the silver nanoparticlecomponent may comprise at least one resin selected from polystyrene,terpene, styrene block copolymers such as styrene-butadiene-styrenecopolymer, styrene-isoprene-styrene copolymer,styrene/ethylen-butylene-styrene copolymer, andstyrene-ethylene/propylene copolymer, ethylene-vinyl acetate copolymers,ethylene-vinyl acetate maleic anhydride terpolymers, ethylene butylacrylate copolymer, ethylene-acrylic acid copolymer, polyolefins,polybutene, polyamides or the like, and mixtures thereof. In certainembodiments, the at least one resin is present in an amount ranging fromabout 0.05 percent to about 5 percent by weight of the total weight ofthe silver nanoparticle component. In certain embodiments, the at leastone resin is present in an amount ranging from about 0.1 to about 3percent by weight of the total weight of the silver nanoparticlecomponent. In other embodiments, the resin is omitted from the silvernanoparticle component.

The silver nanoparticle component may also comprise at least one otheradditive such as humectants, surfactants, and bactericides/fungicides.The additives may be a small percentage with respect to the compositionof the silver nanoparticle component and may be used to tune inkproperties or to add specific properties as is understood by a skilledartisan. For example, at least one surfactant may be included in thesilver nanoparticle component to reduce the surface tension of thesilver component. Viscosity of the silver nanoparticle component may beadjusted to a desired value by including, for example, at least onepolymeric thickening agent such as polyvinyl alcohol. Humectants, suchas glycols, may also be added to the silver nanoparticle component, forexample to control evaporation.

The silver nanoparticle component of a hybrid conductive ink asdisclosed herein may be prepared by any suitable method. One exemplarymethod is to disperse the silver nanoparticles into at least onenon-polar organic solvent and optionally at least one stabilizer underinert bubbling. The silver nanoparticle ink component may then be shakento wet the nanoparticles and then rolled to ensure mixing. The silvernanoparticle ink may then be filtered through a glass fiber andsubsequently purged with nitrogen or argon.

The hybrid conductive inks disclosed herein may be prepared by mixingthe silver nanoparticle component with the eutectic metal alloynanoparticle component. In certain embodiments, the weight ratio of theeutectic metal alloy nanoparticle component to silver nanoparticlecomponent in the hybrid conductive ink may range from about 1:20 (w/w)to about 20:1 (w/w), such as about 1:5 (w/w), about 1:10 (w/w), about1:15 (w/w), about 1:1 (w/w), about 5:1 (w/w), about 10:1 (w/w), or about15:1 (w/w).

The hybrid conductive inks disclosed herein may have any desiredviscosity. In certain embodiments, the viscosity ranges from about 2 cpsto about 500 cps, such as from about 3 cps to about 100 cps, from about4 cps to about 50 cps, or from about 5 cps to about 20 cps. The hybridconductive inks disclosed herein may have any feasible cure rate. Incertain embodiments, the hybrid conductive ink may cure in less thanabout 24 hours, such as between about 10 minutes to about 12 hours orbetween about 1 hour to 3 hours, such as in less than about 2 hours.

Methods of Forming Conductive Elements

The hybrid conductive inks disclosed herein may be used to fabricate aconductive element, such as conductive traces, conductive bonding pads,electrodes, interconnects, and the like.

In certain embodiments, conductive elements may be formed from thehybrid conductive inks by depositing the hybrid conductive ink onto asubstrate and heating the hybrid conductive ink to form annealed silvernanoparticles and melted eutectic metal alloy, wherein the meltedeutectic metal alloy occupies spaces between the annealed silvernanoparticles. In certain embodiments, the deposited hybrid conductiveink is allowed to dry prior to heating.

In certain embodiments, prior to sintering, the hybrid conductive inkmay be deposited onto a substrate, such as a plastic substrate, asdescribed herein. The mixture may then be heated to a temperaturesufficient to sinter the silver nanoparticles, such as, for example,about 130° C. The deposited conductive ink may be electricallyinsulating or may have very low electrical conductivity. However, duringthe sintering process, the silver nanoparticles in the hybrid conductiveink may anneal to form a conductive element. The eutectic metal alloynanoparticles may also participate in the process by melting and flowingbetween the annealed silver nanoparticles to form a conductive “weld” tothe annealed silver.

As used herein, “a temperature sufficient to sinter the silvernanoparticles” is a temperature sufficient to result in attachment ofthe silver nanoparticles at adjacent surfaces. A temperature sufficientto sinter the silver nanoparticles may range, for example, from about80° C. to about 250° C., such as about 145° C. or less, about 140° C. orless, about 130° C. or about 120° C.

The hybrid conductive ink compositions disclosed herein may be depositedonto a substrate or other surface, such as a connective pad, by, forexample, solution depositing. Solution depositing as used herein refersto a process whereby a liquid is deposited upon a substrate to form acoating or pattern. Solution depositing includes, for example, one ormore of spin coating, dip coating, spray coating, slot die coating,flexographic printing, offset printing, screen printing, gravureprinting, ink jet printing, and aerosol jet printing.

In certain embodiments, the hybrid conductive ink is deposited onto asubstrate by ink jet printing. In other exemplary embodiments, aerosoljet printing is used for deposition. As used herein, “aerosol jetprinting” refers to a process that involves atomization of the hybridconductive ink, producing droplets on the order of one to two microns indiameter. The atomized droplets may be entrained in a gas stream anddelivered to a print head. At the print head, an annular flow of gas maybe introduced around the aerosol stream to focus the droplets into atightly collimated beam. The combined gas streams may then exit theprint head through a converging nozzle that compresses the aerosolstream to a small diameter, for example a diameter ranging from about 1micron to about 10 microns. The jet exits the print head and isdeposited on a substrate or other surface. The resulting patterns canhave features ranging from about 5 microns to about 3000 microns wide,with layer thickness ranging from tens of nanometers to about 25microns, such as from about 1 micron to about 20 microns.

The substrates described herein may be any suitable substrate including,but not limited to, silicon, a glass plate, a plastic film, fabric, orsynthetic paper. For structurally flexible devices, plastic substratessuch as polyester, polycarbonate, polyimide, polyethylene terephthalate(PET), polyethylene naphthalate (PEN), and the like may be used. Thethickness of the substrate can be any suitable thickness, such as fromabout 10 micrometers to over 10 millimeters with an exemplary thicknessbeing from about 50 micrometers to about 2 millimeters, such as for aflexible plastic substrate, and from about 0.4 millimeters to about 10millimeters for a rigid substrate such as glass or silicon. In certainembodiments, the flexible plastic substrates is chosen from PET, PEN,and polycarbonate.

The heating for sintering can be for any suitable or desired time, suchas from about 0.01 hours to about 10 hours, such as about 1 hour. Theheating can be performed in air, in an inert atmosphere, for exampleunder nitrogen or argon, or in a reducing atmosphere, for example undernitrogen containing from about 1 to about 20 percent by volume hydrogen.The heating can also be performed under normal atmospheric pressure orat a reduced pressure of, for example, about 1000 mbars to about 0.01mbars.

Heating encompasses any technique that can impart sufficient energy tothe heated material or substrate to anneal the silver nanoparticles andresults in the melting and flow of the eutectic metal alloynanoparticles. These techniques include thermal heating (for example,with a hot plate, an oven, or a burner), infra-red radiation, laserbeam, flash light, microwave radiation, ultraviolet radiation, photonicsintering and combinations thereof. In certain embodiments, an oven isused for heating.

In some embodiments, after heating and cooling, for example to roomtemperature, an electrically conductive element is formed on thesubstrate that has a thickness ranging from about 0.1 to about 20micrometers, such as from about 0.15 to about 10 or from about 0.1 toabout 2 micrometers.

In some embodiments, the conductive element to be formed is aninterconnect. As used herein, an “interconnect” is an interface betweena conductive element (such as wires or copper foil traces or aconductive trace, such as a circuit trace, formed from, for example, aconventional nanosilver ink and/or the hybrid conductive ink asdisclosed herein) and an electronic component such as a capacitor,resistor and/or semiconductor devices, such as diodes, transistors, andintegrated circuits. In certain embodiments, a method of forming aninterconnect comprises depositing, such as by aerosol jet printing orother methods as described herein, the hybrid conductive ink disclosedherein onto a conductive element positioned on a substrate.

The conductivity of the conductive elements, such as an electricallyconductive trace or interconnect, which is produced by heating thedeposited hybrid conductive ink of the present disclosure, may be morethan about 10,000 Siemens/centimeter (S/cm), such as more than about50,000 S/cm, more than about 80,000 S/cm, more than about 100,000 S/cm,more than about 125,000 S/cm, more than about 150,000 S/cm, or more thanabout 200,000 S/cm. In certain embodiments, the conductivity ranges fromabout 50,000 S/cm to about 200,000 S/cm, such as from about 80,000 S/cmto about 150,000 S/cm, or from about 100,000 S/cm to about 125,000 S/cm.

The resistivity of the conductive elements, such as an electricallyconductive trace or interconnect, which is produced by heating thedeposited hybrid conductive ink of the present disclosure may be lessthan about 1.0×10⁻⁴ ohms-centimeter (ohm-cm), less than about 2.0×10⁻⁵ohms-cm, less than about 1.25×10⁻⁵ ohms-cm, less than about 1.0×10⁻⁵ohms-cm, less than about 8.0×10⁻⁶ ohms-cm, less than about 6.6×10⁻⁶ohms-cm, or less than about 5.0×10⁻⁶ ohms-cm. In certain embodiments,the resistance ranges from about 2.0×10⁻⁵ ohms-cm to about 5.0×10⁻⁶ohms-cm, such as from about 1.25×10⁻⁵ ohms-cm to about 6.6×10⁻⁶ ohms-cm,or from about 1.0×10⁻⁵ ohms-cm to about 8.0×10⁻⁶ ohms-cm.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the disclosure are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements. Moreover, all ranges disclosed hereinare to be understood to encompass any and all sub-ranges subsumedtherein.

While the present teachings have been illustrated with respect to one ormore implementations, alterations and/or modifications can be made tothe illustrated examples without departing from the spirit and scope ofthe appended claims. In addition, while a particular feature of thepresent teachings may have been disclosed with respect to only one ofseveral implementations, such feature may be combined with one or moreother features of the other implementations as may be desired andadvantageous for any given or particular function. Furthermore, to theextent that the terms “including,” “includes,” “having,” “has,” “with,”or variants thereof are used in either the detailed description and theclaims, such terms are intended to be inclusive in a manner similar tothe term “comprising.” Further, in the discussion and claims herein, theterm “about” indicates that the value listed may be somewhat altered, aslong as the alteration does not result in nonconformance of the processor structure to the illustrated embodiment. Finally, “exemplary”indicates the description is used as an example, rather than implyingthat it is an ideal.

It will be appreciated that variants of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be combined intomany other different systems or applications. Various presentlyunforeseen or unanticipated alternatives, modifications, variations, orimprovements therein may be subsequently made by those skilled in theart which are also intended to be encompasses by the following claims.

Examples

The following Examples are being submitted to further define variousspecies of the present disclosure. These Examples are intended to beillustrative only and are not intended to limit the scope of the presentdisclosure. Parts and percentages are by weight unless otherwiseindicated.

Example 1—Preparation of Field's Metal Nanoparticles with DifferentOrganoamine Stabilizers A. Butylamine

300 mL of propylene glycol monomethyl ether acetate (PGMEA) solvent wasadded to a 500 mL beaker with a large magnetic bar. The beaker was putinto a water bath on a hot plate. The PGMEA was heated to 65° C. whilestirring the liquid. Next, 60 g (about 83 mL) of butylamine was addedinto the PGMEA. Then 20.8 g of Field's metal (32.5% Bi, 51% In, 16.5%Sn; melting point 62° C.) was added into the mixture, which was mixeduntil the Field's metal totally dissolved, i.e., at least two minutes.The mixture was then sonicated for 8-15 minutes using a Branson DigitalSonifier®, with a probe (Applitude) at 100% power. Ice was put into thewater bath while sonicating to maintain a temperature less than 75° C.The highest temperature reached was about 72° C.

Hot water in the water bath was then decanted, and ice was put into thewater bath; the 500 mL beaker was then put back on the ice. The mixturewas allowed to cool down to room temperature and was left stirringovernight. The stirring was stopped when the mixture cooled down and wassettled. The clear solvent on top of the mixture was then decanted, anda greyish suspension collected. About 500 mL of PGMEA was added tore-disperse the Field's metal nanoparticles in order to wash theresidual amines. The suspension was centrifuged using a BaxterScientific Products Cryofuge 6000 at a speed of 3000 rpm for 15 minutes.The clear solvent on top was decanted, and the washing process wasrepeated one more time. Once the clear PGMEA was decanted, the particleswere left to air dry overnight. The final yield of the particles wasover 95%.

Particle size distribution was analyzed using a Nanotrac® U2275E, andthe results are shown below in Tables 1A and 1B. The average particlesize when butylamine was used as the ligand was 142.6 nm (0.1426 μm),and the median diameter (D50) was 192 nm.

TABLE 1A Particle Size Distribution for Nanoparticles with ButylaminePercentile Size (nm) 10% 124.8 20% 146.0 30% 161.3 40% 176.0 50% 192.060% 212.6 70% 253.1 80% 380 90% 552 95% 674

TABLE 1B Particle Size Distribution for Nanoparticles with ButylamineSize (nm) % Channel % Pass 6,540 0.0 100 5,500 0.0 100 4,620 0.58 1003,890 0.47 99.42 3,270 0.0 98.95 2,750 0.0 98.95 2,312 0.0 98.95 1,9440.0 98.95 1,635 0.0 98.95 1,375 0.0 98.95 1,156 0.0 98.95 972 0.79 98.95818 2.74 98.16 687 4.10 95.42 578 4.91 91.32 486 4.51 86.41 409 4.3881.90 344 3.79 77.52 289 5.38 73.73 243 11.83 68.35 204.4 19.27 56.52171.9 18.19 37.25 144.5 10.24 19.06 121.5 5.25 8.82 102.2 2.95 3.57 85.90.62 0.62 72.3 0.0 0.0 60.8 0.0 0.0 51.1 0.0 0.0 43.0 0.0 0.0 36.1 0.00.0

B. Octylamine

Experiment 1 was repeated twice using octylamine in lieu of butylamineas the organoamine stabilizer. Particle size distribution was analyzedusing a Nanotrac® U2275E for both runs, and the results are shown belowin Tables 2A and 2B and Tables 3A and 3B. The average particle size whenoctylamine was used as the stabilizer was 223.2 nm and 107.5 nm, and theD50 was 339 nm and 191 nm, respectively.

TABLE 2A Particle Size Distribution for Nanoparticles with Octylamine,Run 1 Percentile Size (nm) 10% 207.1 20% 234.0 30% 258.1 40% 285.8 50%339 60% 876 70% 1,064 80% 1,228 90% 1,494 95% 1,812

TABLE 2B Particle Size Distribution for Nanoparticles with Octylamine,Run 1 Size (nm) % Channel % Pass 6,540 0.0 100 5,500 0.0 100 4,620 0.0100 3,890 0.0 100 3,270 0.0 100 2,750 0.0 100 2,312 3.01 100 1,944 4.9596.99 1,635 4.75 92.04 1,375 12.02 87.29 1,156 12.72 75.27 972 3.2462.55 818 1.10 59.31 687 0.60 58.21 578 0.82 57.61 486 1.77 56.79 4094.49 55.02 344 9.51 50.53 289 17.29 41.02 243 14.62 23.73 204.4 5.999.11 171.9 2.20 3.12 144.5 0.69 0.92 121.5 0.23 0.23 102.2 0.0 0.0 85.90.0 0.0 72.3 0.0 0.0 60.8 0.0 0.0 51.1 0.0 0.0 43.0 0.0 0.0 36.1 0.0 0.0

TABLE 3A Particle Size Distribution for Nanoparticles with Octylamine,Run 2 Percentile Size (nm) 10% 97.9 20% 112.1 30% 125.4 40% 143.2 50%191.3 60% 278.8 70% 350 80% 452 90% 1,024 95% 1,615

TABLE 3B Particle Size Distribution for Nanoparticles with Octylamine,Run 2 Size (nm) % Channel % Pass 6,540 0.0 100 5,500 0.0 100 4,620 0.0100 3,890 0.0 100 3,270 0.0 100 2,750 0.0 100 2,312 1.28 100 1,944 3.4698.72 1,635 3.17 95.26 1,375 1.50 92.09 1,156 0.87 90.59 972 1.48 89.72818 2.06 88.24 687 1.89 86.18 578 2.73 84.29 486 4.51 81.56 409 7.9177.05 344 7.80 69.14 289 5.61 61.34 243 4.25 55.73 204.4 4.12 51.48171.9 6.74 47.36 144.5 13.36 40.62 121.5 14.69 27.26 102.2 7.68 12.5785.9 3.14 4.89 72.3 1.75 1.75 60.8 0.0 0.0 51.1 0.0 0.0 43.0 0.0 0.036.1 0.0 0.0

C. Tetraethylenepentamine

Experiment 1 was repeated four times using tetraethylenepentamine inlieu of butylamine as the organoamine stabilizer. Particle sizedistribution was analyzed using a Nanotrac® U2275E, and the results areshown below in Tables 4A and 4B for one of the four trial runs. Theaverage particle sizes when tetraethylenepentamine was used as thestabilizer was 141.4 nm, 148.6 nm, 146.9 nm, and 100.9 nm, for each ofthe four trial runs. The D50 for each each of the four trial runs was179 nm, 193 nm, 201 nm, and 158 nm, respectively.

TABLE 4A Particle Size Distribution for Nanoparticles withTetraethylenepentamine Percentile Size (nm) 10% 121.3 20% 135.6 30%153.3 40% 165.8 50% 179.4 60% 196.2 70% 221.9 80% 260.1 90% 307 95% 342

TABLE 4B Particle Size Distribution for Nanoparticles withTetraethylenepentamine Size (nm) % Channel % Pass 6,540 0.84 100 5,5000.43 99.16 4,620 0.0 98.73 3,890 0.0 98.73 3,270 0.0 98.73 2,750 0.098.73 2,312 0.0 98.73 1,944 0.0 98.73 1,635 0.07 98.73 1,375 0.78 98.661,156 0.12 97.88 972 0.0 97.76 818 0.0 97.76 687 0.0 97.76 578 0.0 97.76486 0.0 97.76 409 2.59 97.76 344 8.62 95.17 289 10.86 86.55 243 11.7975.69 204.4 19.18 63.90 171.9 21.54 44.72 144.5 13.08 23.18 121.5 6.4210.10 102.2 2.87 3.68 85.9 0.81 0.81 72.3 0.0 0.0 60.8 0.0 0.0 51.1 0.00.0 43.0 0.0 0.0 36.1 0.0 0.0

D. Methoxypropylamine

Experiment 1 was repeated using methoxypropylamine in lieu of butylamineas the organoamine stabilizer. Particle size distribution was analyzedusing a Nanotrac® U2275E, and the results are shown below in Tables 5Aand 5B. The average particle size when 3-methoxypropylamine was used asthe stabilizer was 9 nm. The D50 was <1 nm.

TABLE 5A Particle Size Distribution for Nanoparticles withMethoxypropylamine Percentile Size (nm) 10% 0.82 20% 0.84 30% 0.87 40%0.89 50% 0.91 60% 0.93 70% 0.96 80% 0.99 90% 1.04 95% 1.07

TABLE 5B Particle Size Distribution for Nanoparticles withMethoxypropylamine Size (nm) % Channel % Pass 6,540 0.0 100 5,500 0.0100 4,620 0.0 100 3,890 0.0 100 3,270 0.0 100 2,750 0.0 100 2,312 0.0100 1,944 0.0 100 1,635 0.0 100 1,375 0.0 100 1,156 0.0 100 972 0.0 100818 0.0 100 687 0.0 100 578 0.0 100 486 0.0 100 409 0.0 100 344 0.0 100289 0.0 100 243 0.0 100 204.4 0.0 100 171.9 0.0 100 144.5 0.0 100 121.50.0 100 102.2 0.0 100 85.9 0.0 100 72.3 0.0 100 60.8 0.0 100 51.1 0.0100 43.0 0.0 100 36.1 0.0 100 30.4 0.0 100 25.55 0.0 100 21.48 0.0 10018.06 0.0 100 15.19 0.0 100 12.77 0.0 100 10.74 0.0 100 9.03 0.0 1007.60 0.0 100 6.39 0.0 100 5.37 0.0 100 4.52 0.0 100 3.80 0.0 100 3.190.0 100 2.69 0.0 100 2.26 0.0 100 1.90 0.0 100 1.60 0.0 100 1.34 0.0 1001.13 32.06 100 0.95 67.94 67.94

E. Other Ligands

Experiment 1 was repeated using each of 2,2-(ethylenedioxy)diethylamineand pentaethylenehexamine as the organoamine stabilizers. Particle sizedistribution was analyzed using a Nanotrac® U2275E. For2,2-(ethylenedioxy)diethylamine, the average particle size was 0.9 nm,with a D50 of 1 nm. For pentaethylenehexamine, the average particle sizewas 2.9 nm, with a D50 of 212 nm.

Comparative Example 1—Preparation of Field's Metal Particles in Water

300 mL of deionized water was added to a 500 mL beaker with a largemagnetic bar. The beaker was put into a water bath on a hot plate. Thewater was heated to 65° C. while stirring. Next, 60 g (about 83 mL) ofbutylamine was added into the water. Then 20.8 g of Field's metal (32.5%Bi, 51% In, 16.5% Sn; melting point 62° C.) was added into the mixture,which was mixed until the Field's metal totally dissolve, i.e., at leasttwo minutes. The mixture was then sonicated for 8-15 minutes usingBranson Digital Sonifier®, with a probe (Applitude) at 100% power. Icewas put into the water bath while sonicating to maintain a temperatureless than 75° C.

Hot water in the water bath was then decanted and ice was put into thewater bath; the 500 mL beaker was then put back on the ice. The mixturewas allowed to cool down to room temperature and was left stirringovernight. The stirring was stopped when the mixture cooled down and wassettled. The clear solvent on top of the mixture was then decanted, andthe greyish suspension collected. Water was added to redisperse and washthe Field's metal particles from excess amine. The mixture was thencentrifuged at a rpm of 3000 for 15 minutes. The clear water on top wasdecanted after centrifugation. This washing step was repeated once.Finally, after decanting the water, the Field's metal particles wereleft in the beaker to air dry overnight. The final yield of theparticles was greater than 95%.

Particle size distribution was analyzed using a Nanotrac® U2275E. Themeasurements indicated that 95% of the resultant eutectic metal alloyparticles were between 1.3 μm and 5.0 μm. The median diameter (D50) ofthe eutectic metal alloy particles was 4.17 μm.

Example 2—Preparation of Conductive Ink with Field's Metal Nanoparticlesand Organoamine Stabilizers

A 50% solid content ink was prepared as follows: 10.5 g glass beads (d=4mm) were added to a bottle, in addition to 16.7 g of Field's metalnanoparticles, 5.6 g of ethylcyclohexane, and 11.1 g phenylcyclohexane(total solvent=16.7 g). A PTFE cap sealed the bottle. The formulationwas rolled for three days on a movil rod roller.

Example 3—Preparation of Conductive Ink with Field's Metal NanoparticlesOrganoamine Stabilizers and Silver Nanoparticles

12 g of a silver nanoparticle ink was added to a bottle, followed by1.58 g Field's Metal nanoparticles. Argon air was blown into the jar foraround 15 to 20 seconds, and then the bottle was quickly sealed. The inkformulation was rolled for 2 days at about 65 rpm. The ink was printedusing an Optomec Aerosol Jet system, and the conductivity of the printedlines was measured to be about 1.6×10⁵ S/cm.

What is claimed is:
 1. A process for preparing eutectic metal alloynanoparticles comprising: mixing at least one organic polar solvent, atleast one organoamine stabilizer, and a eutectic metal alloy to create amixture; sonicating the mixture at a temperature above the melting pointof the eutectic metal alloy; and collecting from the mixture acomposition comprising a plurality of eutectic metal alloy nanoparticleshaving an average particle size ranging from about 0.5 nanometers toless than about 5000 nanometers.
 2. The process of claim 1, wherein theeutectic metal alloy nanoparticles comprise Field's metal alloy.
 3. Theprocess of claim 1, wherein the at least one organic polar solvent isheated to a temperature ranging from about 30° C. to about 200° C. 4.The process of claim 1, wherein the at least one organic polar solventis chosen from propylene glycol methyl ether acetate, di(propyleneglycol) methyl ether acetate, (propylene glycol) methyl ether,di(propylene glycol) methyl ether, methyl isobutyl ketone, anddiisobutyl ketone.
 5. The process of claim 1, wherein the at least oneorganic polar solvent is propylene glycol methyl ether acetate.
 6. Theprocess of claim 1, wherein the at least one organoamine stabilizer ischosen from propylamine, butylamine, pentylamine, hexylamine,heptylamine octylamine, 3-methoxypropylamine, pentaethylenehexamine,2,2-(ethylenedioxy)diethylamine, tetraethylenepentamine,triethylenetetramine, and diethylenetriamine,1,1-Diamino-3,6,9-trioxaundecane, 2,2′-(Ethylenedioxy)bis(ethylamine),and 2-(2-aminoethoxy)ethylamine.
 7. The process of claim 1, wherein themixture is sonicated for a period of time ranging from about 1 minute toabout 1 hour at about 100% power.
 8. The process of claim 1, wherein theeutectic metal alloy nanoparticles have an average particle size rangingfrom about 50 nanometers to about 800 nanometers.
 9. A hybrid conductiveink composition comprising: a component comprising a plurality of metalnanoparticles; and a component comprising a plurality of eutectic metalalloy nanoparticles and at least one organoamine stabilizer, whereineutectic metal alloy nanoparticles have an average particle size rangingfrom about 0.5 to less than about 1000 nanometers.
 10. The hybridconductive ink of claim 9, wherein the plurality of metal nanoparticlesis silver nanoparticles.
 11. The hybrid conductive ink of claim 10,wherein the silver nanoparticles have an average particle size rangingfrom about 0.5 nanometers to about 100 nanometers.
 12. The hybridconductive ink of claim 9, wherein the eutectic metal alloynanoparticles comprise Field's metal alloy.
 13. The hybrid conductiveink of claim 9, wherein the weight ratio of the eutectic metal alloynanoparticles and the metal nanoparticles ranges from about 1:20 toabout 1:5.
 14. The hybrid conductive ink of claim 9, wherein theviscosity of the hybrid conductive ink ranges from about 2 centipoise toabout 200 centipoise.
 15. The hybrid conductive ink of claim 9, whereinthe eutectic metal alloy nanoparticles have an average particle sizeranging from about 50 nanometers to about 800 nanometers.